1. Field of the Invention
The present invention is directed toward a graphics display system in which a graphics layer is printed upon a transparent substrate so that the graphics are visible therethrough. The inks used to create the graphics layer exhibit excellent adhesion to substrates, such as polycarbonate, and resist degradation by adhesives that might otherwise cause the graphics layer to delaminate from the substrate. In particular embodiments, the inks used to create the graphics layer are UV-curable digital inks capable of being printed onto the substrate by an inkjet printer.
2. Description of the Prior Art
Polycarbonate membrane displays are used in a variety of applications in many industries. Because of its durability, polycarbonate is a good material for use in high-performance environments. Moreover, because it is transparent, one can place an image on the underside, or sub-surface, of the polycarbonate sheet and the image will be protected against damage or wear. Polycarbonate membranes have been employed as overlays in the manufacture of membrane switches which are oftentimes required with withstand millions of switch activations over the product's lifetime. Polycarbonate membrane displays are also typically attached to a mounting surface through the use of a permanent adhesive. Because the image is printed on the sub-surface of the membrane, the ink comes into direct contact with the adhesive. If the adhesive and ink are not properly formulated to be compatible with each other, the adhesive can re-wet the ink thereby resulting in delamination of the ink, and adhesive, from the polycarbonate substrate.
Polycarbonate membrane displays have also been used in the construct of backlit displays, such as those found in automotive interiors. In a backlit display, certain portions of the polycarbonate membrane display are opaque or “blacked out” so that light is permitted to pass through only certain parts of the display. In order to deliver the required opacity, the inks printed upon the polycarbonate membrane must have a high solids and pigment levels. Therefore, such inks have typically been of the screen-printed variety.
Inkjet printing offers the capability to produce on-demand graphics of very high quality. However, until now, digital inks have not been able to provide the performance characteristics necessary to successfully print polycarbonate membrane displays. Presently available digital inks are susceptible to adhesive migration in which the solvents from the adhesive attack and re-wet the ink. This can lead to degradation of image quality over time and failure of the display due to ink delamination. Furthermore, because digital inks are fired through very small nozzles in the inkjet head, it is very difficult to construct an ink having sufficient opacity for use in polycarbonate membrane displays.
In some applications for polycarbonate membrane displays, the membrane may need to be thermally formed into a desired shape, or embossed. Therefore, inks that are highly crosslinked will not stretch or elongate during thermal processing or embossing thereby resulting in the degradation of the graphic's quality.
Accordingly, there is a need in the art for an ink system that can be digitally printed onto a transparent substrate for use in graphics display systems that exhibit excellent adhesion to the substrate, resist adhesive migration, and are capable of elongation along with the substrate during thermal processing.